This invention relates to an in-tank fuel supply unit for supplying fuel from a motor vehicle fuel tank to the vehicle engine.
In-tank fuel pumps have been well known for some time. In order to ensure that there is always sufficient fuel available at the pump inlet, it is known to locate the pump in a reservoir within the tank, and to make use of a so-called jet pump to maintain a certain fuel level within the reservoir, whatever the level of fuel in the tank.
A jet pump makes use of the venturi effect by directing a high speed jet of liquid through an orifice so that the jet entrains liquid from around the orifice and pumps that liquid through the orifice.
An example of a fuel supply unit with a jet pump is shown in U.S. Pat. No. 5,341,842.
It is self-evident that the jet pump must refill the reservoir at least as fast as fastest rate at which fuel is withdrawn from the reservoir by the pump. It is therefore necessary to make the jet pump as efficient as possible.
It is also desirable to make such fuel supply units as compact as possible, and for them to be economic to manufacture in large quantities.
According to the invention, an in-tank fuel supply unit for supplying fuel from a fuel tank to a motor vehicle engine, includes a reservoir to be mounted within a fuel tank, a fuel pump mounted in the reservoir and adapted to draw fuel from the reservoir, a fuel outlet from the pump and two fuel passages connected to the outlet, one of the passages feeding fuel to the engine, and the other passage feeding fuel to a jet pump, wherein the jet pump comprises a nozzle arranged to inject fuel into a venturi, the nozzle and the venturi being arranged on a vertical axis with the nozzle injecting fuel upwards into the venturi.
Directing the venturi upwards saves space in the reservoir in a horizontal plane, but more importantly the fact that the flow from the nozzle into the reservoir is all in a straight line helps to enhance the performance of the venturi.
The venturi passage is preferably formed integrally with the reservoir, as a molded part, and has a converging section followed by a parallel-sided section followed by a diverging section. This form of the venturi passage has a big influence on venturi performance.
The venturi nozzle is preferably manufactured separately from the reservoir and is molded from a plastics material different from that of the reservoir and venturi passage. By molding the nozzle separately from the passage and the reservoir it becomes possible to optimize the materials for each part. In addition, the combination of a vertical venturi path and a separately molded nozzle allows for access to both ends of the venturi passage during molding so that the converging and diverging sections can be correctly and accurately molded.
The nozzle diameter is preferably in the range of about 0.35-0.5 mm and most preferably 0.45 mm. The nozzle length is preferably between about 1 and 2 mm, and most preferably 1.5 mm.
The distance from the tip of the nozzle to the mouth of the venturi passage is preferably between about 4 and 6 mm.
The included angle of the converging section is preferably between about 50 and 70xc2x0; the length of the parallel section of the venturi passage is preferably between about 7 and 10 mm and the diameter is preferably between about 4 and 6 mm; and the included angle of the diverging section is preferably between about 8 and 12xc2x0.
The dimensional ranges proposed have been chosen to optimize venturi performance.